The present application relates to a battery pack for use in an electrically powered tool or the like, in which a load rush current flows, and a method of controlling a battery pack.
In recent years, as the power sources of various electronic apparatuses, a lithium-ion secondary battery which has advantages, such as high power, high energy density, compact, and lightweight, is widely used. The lithium-ion secondary battery has high energy density as compared with other secondary batteries using, for example, nickel-cadmium or nickel-hydride, so it is very important to ensure sufficient safety of the battery.
In a battery pack using a lithium-ion secondary battery, when an output is short-circuited for any reason, an internal part may be damaged due to overcurrent. While the charge/discharge cycle is repeated, the battery may be deteriorated due to overcharge or overdischarge, and heat may be abnormally generated. For this reason, a protection circuit or a protection IC (Integrated Circuit) is generally mounted in the battery pack so as to inhibit charge/discharge at the time of overcurrent, or overcharge or overdischarge.
In such a protection circuit, a predetermined threshold value is set in advance as an overcurrent detection current with respect to a charge/discharge current, when the value of the detected charge/discharge current exceeds the threshold value, it is determined to be an overcurrent, and charge/discharge is inhibited.
An existing battery pack is provided with, for example, a charge control FET (Field Effect Transistor) and a discharge control FET (hereinafter, appropriately referred to charge/discharge control FET). A charge/discharge current is detected on the basis of a potential difference between both ends of a source-drain resistor of the charge/discharge control FET. For example, JP-A-2000-67928 describes a technique in which a current is detected on the basis of a voltage drop due to the on resistance of the discharge control FET